Low temperature bonding material comprising metal particles and bonding method

ABSTRACT

A bonding material comprising metal particles coated with an organic substance having carbon atoms of 2 to 8, wherein the metal particles comprises first portion of 100 nm or less, and a second portion larger than 100 nm but not larger than 100 μm, each of the portions having at least peak of a particle distribution, based on a volumetric base. The disclosure is further concerned with a bonding method using the bonding material.

CLAIM OF PRIORITY

The present application claims priority from Japanese application serialNo. 2006-353649, file on Dec. 28, 2006, the content of which is herebyincorporated by reference into this application.

FIELD OF THE INVENTION

The present invention relates to a low temperature bonding material forbonding electronic parts and a method for bonding the electronic partsusing the bonding material.

RELATED ART

In non-insulated type semiconductor devices such as power semiconductordevices that are used for inverters, etc, a member for fixing thesemiconductor tips is an electrode through which electric current ofseveral amperes or more flows heat at the time the semiconductor deviceis in operation so that the semiconductor chip generates. Recently,since a current capacity of the semiconductor device is increasing, anamount of heat at the mounting portion of the semiconductor device, i.e.die-bonding portion is increasing.

In order to stably operate the semiconductor chip while avoidingreduction in life and instability of characteristics due to the heat, itis necessary to secure heat dissipation at soldered portions andlong-term reliability (heat resistance) of the semiconductor chipmounting portions. Accordingly, a bonding material which is excellent inhigh heat dissipation and heat resistance is needed.

On the other hand, in insulated type semiconductor devices it isnecessary to effectively dissipate heat generating at the time ofoperation of the semiconductor devices to outside thereof and to securebonding reliability of the soldered portions.

Patent document No. 1 discloses a bonding method wherein metal particlescoated with organic substance and having a particle size of 100 nm orless is used, and the organic substance covering the metal particles isdecomposed at the time of heating and pressurizing to thereby effectsintering phenomenon among the metal particles. In this technology, themetal particles after bonding transform into bulk metal and at the sametime metallic bonding in the bonding interface of bonding takes place.

Patent document No. 2 discloses that in a bonding method using metalparticles having a particle size of 100 nm or less, the metal particleshaving the particle size of 100 nm or less is mixed with particleshaving a particle size of 1 to 100 μm thereby to secure a thickness ofthe bonding layer.

Nowadays a change from solder material containing lead to lead-freesolder has been urged; however, substituents for high temperature solderhave not been provided so far. Since it is necessary to utilizehierarchy solders to perform package of electronic parts, a bondingmaterial for substituents of the high temperature solder has beendesired. Accordingly, the bonding technology utilizing the metalparticles having the particle size of 100 nm or less is expected to besubstituents for the high temperature solders.

-   Patent document No. 1: Japanese patent laid-open 2004-107728-   Patent document No. 2: Japanese patent laid-open 2005-136375

SUMMARY OF THE INVENTION

The present invention is featured by a bonding material comprising metalparticles coated with an organic, wherein the metal particles comprises(1) particles having a particle size of 100 nm or less and (2) metalparticles having a particle size larger than 100 nm but not larger than100 μm, and wherein there is at least one peak in each of particledistributions of the metal particles (1) and (2) in a volumetric unit.

A bonding material according to another aspect of the present inventioncomprises metal particles having a particle size of 1 nm to 100 nm andaggregates of the metal particles, wherein aggregates have a grain sizeof 10 nm to 100 μm.

A still another aspect of the present invention is featured by a methodof bonding electrodes of an electronic part and winding circuits of awiring board, which comprises coating a bonding material comprisingmetal particles coated with an organic substance and having a particlesize of 100 μm, wherein the metal particles comprises (1) particleshaving a particle size of 100 nm or less and (2) metal particles havinga particle size more than 100 nm to 100 μm, and wherein there is atleast one peak in each of particle distributions of the metal particles(1) and (2) in a volumetric unit on a bonding face between the circuitsand the electrodes, and heating and pressurizing the circuits,electrodes and the bonding material to thereby bond the circuits and theelectrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a relationship between heating temperatures and residualweight;

FIG. 2 shows a relationship between bonding temperatures and shearingstrength;

FIG. 3 shows a relationship between the number of carbon atoms in theorganic substances used for coating silver particles and shearingstrength;

FIG. 4 shows a structure of a non-insulated type semiconductor deviceaccording to an embodiment of the present invention, wherein FIG. 4( a)a plan view of the device and FIG. 4( b) is a cross sectional view alongline A-A′ in FIG. 4( a);

FIG. 5 shows a sub-assembly of the insulated type semiconductor deviceshown in FIG. 4;

FIG. 6 shows a cross sectional view of a sub-assembly of the insulatedtype semiconductor device shown in FIG. 5, before bonding;

FIG. 7 shows a perspective view of a non-insulated type semiconductordevice according to another embodiment;

FIG. 8 shows a cross sectional view of the semiconductor device shown inFIG. 7, before bonding;

FIG. 9 shows an embodiment of a non-insulated type semiconductor devicesimilar to that of example 3 in which FIG. 9( a) is a plan view of thesemiconductor device and FIG. 9( b) is a cross sectional view of thesemiconductor device shown in FIG. 9( a);

FIG. 10 shows a cross sectional view of the insulated type semiconductordevice; and

FIG. 11 shows a cross sectional view of the mini-molded typenon-insulated semiconductor device according to an example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the bonding technologies disclosed in Patent document Nos. 1 and 2,which use metal particles having a particle size of 100 nm or less,bonding at the bonding interface is performed by metallic bonding. As aresult, high heat resistance, reliability and high heat dissipation areexpected. On the other hand, the fine metal particles having a particlesize of 100 nm or less tend to aggregate. Therefore, it is necessary tocoat the metal particles with an organic material to stabilize the finemetal particles. In the conventional technologies, in order to stabilizethe metal particles more stable organic materials such asalkylcarboxylic acid having a long chain have been used as a coatingmaterial. The protecting coating of the organic material must be removedat the time of bonding; however, the protecting coating is not removedcompletely by low temperature heating, which leads to insufficient shearstrength. Accordingly, in order to obtain sufficient share strength theheating temperature is elevated or the heating time must be extended.However, it is necessary to lower the temperature for heat treatment andshorten the heating time so as to avoid damage to the electronic partsduring the bonding process. In the bonding process using the metalparticles having a particle size of 100 nm or less, low temperature andshort time bonding have not been investigated.

The present invention aims at providing a bonding material and a bondingmethod that are capable of lowering the heating temperature andshortening the heating time during the bonding process, and alsoproviding a semiconductor package free from deterioration of long termreliability under a high temperature atmosphere.

In the following the embodiments of the present invention will beexplained in detail.

The present invention utilizes a phenomenon that sintering of fine metalparticles having a particle size of 100 nm or less takes place. Thebonding material of the present invention comprises metal particleshaving a particle size of 100 nm or less, the particles being coatedwith organic substance having carbon atoms of 2 to 8, wherein there area first particle group of 100 nm or less and a second particle of 100 nmto 100 μm each having at least one peak of a particle size distributionbased on volumetric unit.

In the present invention, the organic substance for coating the metalparticles has carbon atoms of 2 to 8. FIG. 1 shows a relationshipbetween heating temperatures and residual weight according to thermalweight measurement with respect to organic substances including hexylamine having 6 carbon atoms, octyl amine having 8 carbon atoms, decylamine having 10 carbon atoms, laulyl amine having 12 carbon atoms.According to FIG. 1, it is apparent that the smaller the number ofcarbon atoms of the organic substances, the lower the thermal weightloss starting temperature becomes. Accordingly, it is possible to lowerthe decomposition temperature for decomposition by using the organicsubstance having a short chain of the small number of carbon atoms.Therefore, by coating the metal particles with the organic substanceshaving 2 to 8 carbon atoms, the decomposition and removal of the organicsubstance can be done at lower temperatures. That is, the bondingtemperature can be lowered.

If the number of carbon atoms of the organic substance is smaller than2, the metal particles aggregate at room temperature; the metalparticles are not coated in a stable state. If the number of carbonatoms exceeds 8, the decomposition temperature is too high, andsintering of the metal particles is suppressed at the bonding process tothereby lower the shear strength. Accordingly, the number of carbonatoms in the organic substance is 2 to 8.

Since the organic substance for coating the metal particles becomes acomponent that suppresses sintering of the metal particles after thebonding, it is necessary to make an amount of residue of the organicsubstance in the bonding layer as small as possible. Therefore, it isnecessary to make the amount of organic substance as small as possibleso as to sufficiently decompose and remove it under low temperature.

The present inventors have found that after investigation on the metalparticles coated with the organic substance containing carbon atoms of 2to 8, the metal particles comprise not only particles having a particlesize of 100 nm or less (first particles) but also particles having 100nm to 100 μm (second particles), wherein the first and second particleshave particle size distributions based on volumetric unit each having atleast one peak. The metal particles having the particle size of 100 nmto 100 μm should preferably be coated with the organic substance becausedispersing capability of the metal particles having the particle size of100 nm to 100 μm with the metal particles having the particle size of100 nm or less is better than the case where the metal particles havingthe particle size of 100 nm to 100 μm that is not coated with theorganic substance is admixed with the metal particles having theparticle size of 100 nm or less.

The metal particles having the particle size of 100 nm to 100 μm can beparticles that are aggregated metal particles having the particle sizeof 100 nm or less. In this case, because the organic substance coated onthe metal particles having the particle size of 100 nm or less and thecoated metal particles having the particle size of 100 nm to 100 μm isthe same one, a better dispersing capability in an organic solvent isexpected.

Shapes of the aggregates of the metal particles may have differentshapes such as globular, elliptic, triangle, rectangular forms, etc,which are formed by random unification of metal particles. The shapes ofthe aggregates are not limited to the above ones. The aggregates ofmetal particles having the particle size of 1 nm to 100 nm shouldpreferably have a particle size of 10 nm to 100 μm.

As described above, by employing metal particles having peaks in therange of a particle size of 100 nm or less and a range of a particlesize larger than 100 nm, a shear strength can be increased. Although thedetailed mechanism for increasing the shear strength is not elucidatedyet, it is considered that the metal particles of 100 nm or less fillgaps among metal particles of 100 nm or more in the bonding material toeffect sintering at low temperatures thereby to enhance sintering of themetal particles of a particle size of 100 nm or more. Further, acombination of the metal particles having a peak in a range of 100 nm orless and a peak in a range of 100 nm or more reduces an amount of theorganic substance in the bonding material, which leads to bettersintering of the bonding material to reduce a residue of the organicsubstance. As a result, a high shear strength is obtained.

A mixing ratio (% by weight) of the metal particles of 100 nm or less tothe metal particles of 100 nm or more is preferably more than 0.1% byweight, but less than 100%. If the amount of the metal particles of 100nm or less is 0.1% or less, the gaps among the metal particles of 10 nmor more would not be filled with the metal particles of 10 nm or less.As a result, the shear strength will be lowered.

The metal particles used in the present invention and having a particlesize of 100 nm or less are selected from the group of gold, silver,copper, platinum, palladium, rhodium, osmium, ruthenium, iridium, iron,tin, zinc, cobalt, nickel, chromium, titanium, tantalum, indium,silicon, aluminum, etc or alloys thereof. Particularly, Au or Au alloys,Ag or Ag alloys are preferably used singly or combinations thereof.

The metal particles having a particle size of 1 to 100 μm are selectedfrom Au, Au alloys, Ag, Ag alloys, nickel metal core metal plated withAu or Au alloys, Ag or Ag alloys, or copper core metal plated with Au,Au alloys, Ag, Ag alloys, etc.

The organic substance having carbon atoms of 2 to 8 for coating themetal particles contains radicals that are capable of formingcoordination with the metal elements and include oxygen atoms, nitrogenatoms or sulfur atoms. For example, there are exemplified an aminogroup, alcohol group, carboxylic group, sulfanyl group, carbonyl group,aldehyde group, etc.

Alkyl amines are useful compounds. For example, there are butyl amine,pentyl amine, hexyl amine, heptyl amine and octyl amine. The aminecompounds may have a branched structure; for example, there are2-ethylhexyl amine, 1,5-dimethylhexyl amine, etc. In addition to primaryamines, secondary amines and tertiary amines are usable. The organicsubstance may have a cyclic structure.

Carboxylic compounds such as alkyl carboxylic acids are usefulcompounds. For example, there are butanoic acid, pentanoic acid,hexanoic acid, heptanoic acid and octanoic acid. In addition to theprimary carboxylic acids, secondary carboxylic acids and tertiarycarboxylic acids, dicarboxylic acids, cyclic carboxylic acids areusable.

Alcohol group containing compounds such as alkyl alcohols are usable.For example, there are ethanol, propyl alcohol, pentyl alcohol, heptylalcohol and octyl alcohol. In addition to the primary alcohols,secondary alcohols, tertiary alcohols, alkane diols, cyclic alcohols areusable. Further, citric acid, ascorbic acid are usable.

Sulfanyl group containing compounds such as alkylthiols are usefulcompounds. For example, there are 1-thylthiol, 1-propyl thiol,1-butylthiol, 1-pentylthiol, 1-hexylthiol, 1-heptylthiol and1-ocylthiol. Secondary thiols and tertiary thiols may be used.

In addition to the above compounds, compounds containing carbonyl group,aldehyde group and ester group and having carbon atoms of 2 to 8 can beused as a protecting film. The compounds can be used singly or incombination.

The bonding material according to the present invention may be used in aform of paste wherein the metal particles coated with the organicsubstance are dispersed in an organic solvent. Examples of the organicsolvents are alcohols such as methanol, ethanol, octyl alcohol, ethyleneglycol, triethylene glycol, α-terpineol, etc, and hexane, heptane,octane, decane, dodecane, cyclopentane, cyclohexane, benzene, toluene,xylene, ethylbenzene, water, etc.

The bonding materials comprising the metal particles having the particlesize of 100 nm or less, wherein the metal particles having the particlesize of 100 nm or less and the metal particles having the particle sizelarger than 100 nm to 100 μm respectively have peaks in a volumetricbase is prepared by aggregating the metal particles having the particlesize of 100 nm or less. The metal particles having the particle size of100 nm or less can be prepared by any conventional methods in which themetal particles having the particle size are synthesized in a solution.The metal particles coated with the organic substance and having theparticle size of 100 nm or less, produced in the methods, subjected toremoving a solvent with an evaporator. As a result, aggregation of themetal particles takes place to thereby form the bonding materialcomprising the metal particles of 100 nm or less and metal particleslarger than 100 nm to 100 μm, the metal particles having peaks in thevolumetric base.

In order to aggregate the metal particles having the particle size of100 nm or less to impart a particle size distribution, the metalparticles coated with the organic substance having carbon atoms of 2 to8 can be heated, the organic substance is removed with an organicsolvent, or ultraviolet ray is irradiated on the metal particles tovaporize the organic substance, in addition to the abovementioned-method. The method for aggregation of the metal particles arenot limited to the above.

The bonding material can be admixed with flake form silver metal and athermosetting resin such as epoxy resin, polyimide resin, etc. Theresins are not limited to the above ones. In order to obtain strongbonding by the bonding material, an amount of the metal particles shouldpreferably be larger than 50 parts by weight, but lower than 99 parts byweight, based on the total weight of the bonding material.

Next, a bonding method using the bonding material of the presentinvention will be explained.

In a method of bonding electrodes with circuit wiring of a wiring board,the above-described bonding material was coated at bonding faces of thecircuit wiring and electrodes, and electronic elements were mounted onthe circuit wiring. Followed by heating and pressuring the bonding facesto perform bonding.

A heating temperature was preferably 40° to 400° C. The heatingtemperature of 40° C. or higher was necessary to remove the organicsubstance coated on the metal particles within a reasonable time period.A pressuring time was 60 minutes or less. If the pressure time is longerthan 60 minutes, it takes too much time to produce a product, which isnot proper for mass production.

When the bonding material is used as a paste material for brazing, thereare various methods exemplified below.

-   (1) An ink-jet method wherein the paste is coated on the bonding    portion or the electrodes on a substrate by jetting the paste    through a fine nozzle.-   (2) A method for coating the paste through a metal mask or mesh-form    mask, having a necessary opening.-   (3) A method of coating the paste using a dispenser.-   (4) A method of coating the water repellent resin through an opening    of a metal mask or a mesh-form mask.-   (5) A method of coating a photosensitive resin on a surface    including the bonding portion, followed by exposing and developing    the bonding portion. Then, the exposed portion is coated with the    paste.-   (6) A method of coating a water repellent resin on the surface    including the bonding portion of a substrate or the electronic    elements, followed by removing the water repellent resin on an    unnecessary part to form openings. Then, the paste is coated in the    openings.

The coating method is selected in accordance with area to be bonded andshapes of the bonding portions.

In the following, examples according to the present invention will beexplained.

Examples 1-2, Comparative Examples 1-2

In example 1 Ag particles were coated with hexyl amine; in example 2 Agparticles were coated with octyl amine; in comparative example 1 Agparticles were coated with decyl amine; and in comparative example 2 Agparticles were coated with lauryl amine.

The Ag particles coated with hexyl amine in example 1 has peaks ofparticle size at 7.6 nm and 15.2 nm in a range of 100 nm or less, and apeak of particle size at 0.3437 μm in a range of 100 nm or more. The Agparticles coated with octyl amine in example 2 has peaks of particlesize at 7.6 nm and 15.2 nm in a range of 100 nm or less, and a peak ofparticle size at 2.75 μm in a range of 100 nm or more.

The Ag particles coated with decyl amine in comparative example 1 haspeaks of particle size at 7.6 nm and 15.2 nm in a range of 100 nm orless. The Ag particles coated with lauryl amine in comparative example 2has a peak of particle size at 18.1 nm.

The above-mentioned 4 kinds of Ag particles were subjected to particledistribution measurement by dispersing the Ag particles in toluene. Theparticle distribution measurement was conducted by a micro-track ultrafine particle distribution meter 9340-UPA150 manufactured by Nikkiso,Ltd. Measurement was repeated three times and an average value wasdetermined.

On the other hand, thermogravimetric analysis on 4 kinds of organicsubstances for coating the Ag particles, i.e. hexyl amine, octyl amine,decyl amine and lauryl amine was conducted. For measurement of thethermogravimetry, TG/DTA6200 manufactured by Seiko Instruments was used.A temperature rise was 10° C./min and measurement was carried out inair.

As shown in FIG. 1, hexyl amine having 6 carbon atoms in example 1 andoctyl amine having 8 carbon atoms in example 2 exhibited lowerthermogravimetric decrease temperatures than those of decyl amine having10 carbon atoms in comparative example 1 and lauryl amine having 12carbon atoms in comparative example 2. From these results, the smallerthe number of carbon atoms of the organic substance, the lower thesintering temperature of the metal powder becomes.

The Ag particles coated with hexyl amine in example 1 having a particlesize of 100 μm was prepared by dispersing Ag particles in 200 mL oftoluene solvent together with 4.0 g of silver nitrate and 5 g of hexylamine and the solution was stirred. Then, 4 g of ascorbic acid wasadded, followed by stirring for 1 hour and a half to thereby prepare Agparticles having a particle size of 100 nm or less and coated with hexylamine. Thereafter, filteration of the solution was conducted usingquantitative filter paper (No. 5) to remove unreacted ascorbic acid andsilver nitrate.

Further, added was about 200 mL of acetone solvent to the toluenesolution of the filtered product of silver particles whose surface wascoated with hexyl amine and has a particle size of 100 nm or less so asto precipitate the silver particles. After removing the supernatant,purification was conducted by removing excess hexyl amine andby-products produced at the reaction. These processes were repeatedthree times. The repetition of the processes removes the organicsubstance covering silver particles and aggregation of the silverparticles of the particle size of 100 nm or less proceeds to producesilver particles having a particle size of 100 nm or more.

As the number of carbon atoms of the organic substance covering thesurface of the silver particles decreases, a distance among the silverparticles becomes small so that silver particles may directly contactwith each other. Further, because the low carbon atom organic substanceshave low volatile temperatures, and because the low carbon atom organicsubstance may separate from the silver particles, the silver particlestend to aggregate more easily than high carbon atom organic substances.

After evaporating the organic solvent of the resulting silver particleswith an evaporator having 40° C. water bath, 2.5 g of silver particleswas obtained. It is possible to effect aggregation of silver particlesby changing a liquid state to a powder state.

Thereafter, the silver particles were re-dispersed in toluene solvent tothereby produce a dispersion wherein silver particles coated with hexylamine are dispersed. In example 2, octyl amine was used to producesilver particles covered with octyl amine, which are dispersed intoluene solvent in the same manner as in example 1.

On the other hand, silver particles dispersed in toluene solvent wereobtained in comparative examples 1 and 2 using decyl amine and laurylamine in the same manner as in example 1.

Measurement of particle distribution of the silver particles obtained inexamples 1 and 2 and comparative examples 1 and 2 was conducted. Theresults are shown in Table 1. The four kinds of the silver particles hadthe particle distributions shown in Table 1 and had the organicsubstance carried on the surface of silver particles that have thermaldecomposition characteristics shown in FIG. 1.

TABLE 1 Comparative Comparative Example 1 Example 2 Example 1 example 2Hexyl amine Octyl amine Decyl amine Lauryl amine *1 7.6 7.6  7.6 18.115.2 15.2 15.2 *2 0.344 2.75 No peak No peak *1; Particle size (nm) atpeaks in a range of 100 nm or less *2; Particle size (nm) at peaks in arange of 100 nm or more

Next, shearing strength tests of bonded portions were conducted whereina paste material dispersing the silver particles in toluene was used.Test pieces were made of copper. An upper member had a diameter of 5 mmand a thickness of 2 mm; a lower member had a diameter of 10 mm and athickness of 5 mm. After the paste material was coated on the testpieces, drying at 60° C. for 5 minutes was conducted to remove toluene,followed by bonding. Bonging temperatures were selected as 250° C., 300°C., 350° C. and 400° C. Bonding time was 2 minutes 30 seconds. Apressure was 2.5 MPa.

Using the test pieces obtained in the above bonding methods, shearstrength under a single shearing stress was measured. In the shearingtest Bond Tester—SS-100KP (maximum load; 100 kg) manufactured by SeishinTrade Corp. was used. A shearing speed was 30 mm/min, and the testpieces were ruptured by a shearing tool to measure the maximum load atrupture. The maximum load was divided by a bonding area to obtain thesharing strength. The bonding temperatures in FIG. 2 were 250□, 300□,350□ and 400□.

The shearing strength of the bonding portion using laurylamine fortreating the silver particles of the paste was 100%, and ratios ofshearing strengths of the bonding portions using decylamine, octylamineand hexylamine to the shear strength of the bonding portion usinglaurylamine.

In FIG. 3 there is shown a relationship between the number of carbonatoms in the organic substances used for coating silver particles andshearing strength. As the number of carbon atoms coated on the silverparticles deceases, and the particle size distribution based on avolumetric base has a peak in a particle size of 100 nm or more, theshear strength becomes large. When the number of carbon atoms is 8 orless, and when a bonding material wherein aggregation of silverparticles progresses is used, residue of the organic substance in thesintered layer decreases after bonding and the shear strength starts toincrease. When the number of carbon atoms is 6, sufficient sinteringprogresses to produce a strong bonding.

Example 3

FIG. 4 shows s structure of a non-insulated type semiconductor deviceaccording to an embodiment of the present invention, wherein FIG. 4( a)a plan view of the device and FIG. 4( b) is a cross sectional view alongline A-A′ in FIG. 4( a).

After the semiconductor (MOSFET) 301 is mounted on ceramic insulatingsubstrate 302, which is mounted on base 301, epoxy resin case 304,bonding wire 305 and epoxy resin cover 306 were arranged. Silicone gel307 was filled in the case 304. The ceramic insulating substrate 302 onthe base 303 was bonded with a bonding layer 308 formed by the paste ofexample 1. The paste comprises silver particles having the particle sizeof 100 μm or less, which were coated with hexylamine, and have peaks at7.6 nm and 15.2 nm when the volumetric base particle distribution is 100nm or less, and at 0.3437 μm when the volumetric base particledistribution is 100 nm or more. The silver particles were dispersed intoluene in a concentration of 80% by weight to form the bonding layer308.

8 of Si MOSFETs were bonded by the bonding layer 309 formed from theabove-mentioned paste on copper plate 302 a of the ceramic insulatingsubstrate 302. Bonding was carried out by the bonding layers 308, 309formed from the above-mentioned paste, wherein the paste was coated onthe copper plate 302 a (Ni plated) on the ceramic insulating substrate302, and was coated on the base material 303.

The semiconductor elements 301 and the ceramic insulating substrate 302were placed on the coated paste. The bonding portions were heated at300° C. for 5 minutes under a pressure of 0.5 MPa.

Electrodes 302 b formed on the insulating substrate and terminals 310formed to the epoxy resin case 304 were connected by aluminum bondingwire having a diameter of 300 μm, bonded by ultrasonic bonding. Athermistor element 311 for detecting temperature has a bonding layer 309formed from the paste. Electrode 302 and terminal 310 are connected byaluminum bonding wire 305 having a diameter of 300 μm to be connected tooutside.

The epoxy resin case 304 and the base material 303 were fixed withsilicone resin adhesive (not shown). The thick portion of the epoxyresin cover 306 has a cavity 306′, and the terminal 310 has a hole 310′;a screw (not shown) for connecting the insulated type semiconductordevice 1000 to an outer circuit can be disposed. The terminal 310 waspunched into a desired shape in advance. The shaped copper plate was Niplated, which was fixed to the epoxy resin case 304.

FIG. 5 shows a sub-assembly of the insulated type semiconductor deviceshown in FIG. 4, wherein the ceramic substrate and the semiconductorelement were mounted on the base material 303 as a composite material.The base material 303 is provided with fixing holes 303A in theperiphery of thereof. The base material is formed of copper, the surfaceof which is plated with Ni.

The base material 303 was coated with the paste used in example 1. Thepaste comprises silver particles coated with hexylamine; the silverparticles having the particle size of 100 nm or less have particle sizedistribution peaks at 7.6 nm and 15.2 nm and in a particle size of 100nm or more the silver particles have a peak of the particle sizedistribution at 0.344 μm. The silver particles having the above particledistribution peaks were dispersed in toluene at a concentration of 80%by weight. MOSFET 301 was mounted on the ceramic insulating substrate302 by the paste.

FIG. 6 shows a cross sectional view of a sub-assembly 1000 of theinsulated type semiconductor device shown in FIG. 5, before bonding. Asshown in FIG. 6, it is possible to use the paste material in which thebonding material in example 1 is dispersed in toluene in a concentrationof 80% by weight. For preventing flowing out of the paste at the time ofcoating, a water repellent film 322 was formed in correspondence to themounting area of the ceramic insulating substrate 302 on the basematerial 303.

Experiment 4

FIG. 7 shows a perspective view of a non-insulated type semiconductordevice according to another embodiment.

The semiconductor element 701 and ceramic insulating substrate 703 werebonded by the paste used in example 1 wherein the paste comprises silverparticles coated with hexylamine; the silver particles having theparticle size of 100 nm or less have particle size distribution peaks at7.6 nm and 15.2 nm and in a particle size of 100 nm or more the silverparticles have a peak of the particle size distribution at 2.75 μm. Thesilver particles having the above particle distribution peaks weredispersed in toluene at a concentration of 80% by weight.

The emitter electrode of the semiconductor element and the copper wiringplated with nickel, formed on the ceramic insulating substrate, werebonded by the paste.

FIG. 8 shows a cross sectional view of the semiconductor device shown inFIG. 7, before bonding. Connecting terminal 731 was copper plate platedwith nickel and gold on nickel plating. After mounting the semiconductorelement 701 on the wiring 702 a of the insulating substrate, the pastematerial (710) was coated on the emitter electrode (upper side). Then, agold plated portion of the copper wiring 702 b formed on the insulatingsubstrate 702 the surface of which was nickel-plated and a portionbetween the emitter electrode and the terminal 731 were coated with thepaste (709). The connecting terminal 731 was placed on electrode abovethe paste material and bonding between the semiconductor 701 and theinsulating substrate 702 b was conducted at 250° C. under a pressure of1.0 MPa for 5 minutes. In the insulated type semiconductor device, sincelarge current flows through not only the collector electrode, but alsothe emitter electrode, it is possible to increase bonding reliability atthe emitter electrode side by using a connecting terminal 731 having alarge wiring width.

Example 5

FIG. 9 shows an embodiment of a non-insulated type semiconductor devicesimilar to that of example 3. FIG. 9( a) is a plan view of thesemiconductor device and FIG. 9( b) is a cross sectional view of thesemiconductor device shown in FIG. 9( a). In this example, a connectingterminal 505 was used instead of the bonding wire in example 3.

The electrodes 302 a, 302 b on the insulating substrate and terminal 310formed on epoxy resin casing 304 were bonded by using a paste used inexample 1. The paste was coated on the electrodes. The bonding wasconducted by heating at 250° C. for 2 minutes under a pressure of about0.5 MPa towards the clip 505.

The paste comprises silver particles coated with hexylamine; the silverparticles having the particle size of 100 nm or less have particle sizedistribution peaks at 7.6 nm and 15.2 nm and in a particle size of 100nm or more the silver particles have a peak of the particle sizedistribution at 2.75 μm. The silver particles having the above particledistribution peaks were dispersed in toluene at a concentration of 80%by weight.

Example 6

In this example there is explained an insulated type semiconductordevice for a high frequency amplification apparatus used in atransmitter of cellular telephones, etc.

The insulated type semiconductor device (size: 10.5 mm×4 mm×1.3 mm) inthis example has a following constitution. FIG. 10 shows a crosssectional view of the insulated type semiconductor de vice. MOSFETelement 1 (size: 2.4 mm×1.8 mm×0.24 mm), chip resistor 101 (temperaturecoefficient about 7 ppm/° C.) and chip condenser 102 (temperaturecoefficient about 11.5 ppm/° C.) were mounted on a multi-glass ceramicsubstrate 100 as a substrate (size: 10.5 mm×4 mm×0.5 mm; three layeredwiring; thermal expansion coefficient 6.2 ppm; thermal conductivity 2.5W/m·K; bending strength 0.25 Gpa; Young's modulus 110 Gpa; specificdielectric constant 5.6 (at 1 MHz)).

An intermediate metal member 103 such as Cu—Cu2O composite material isdisposed between MOSFET element 1 and the multi-layered glass ceramicsubstrate 100. There are formed inside of the multi-layered glassceramic substrate 100 a thick film inner wiring layer (Ag-1 wt % Pt,diameter 140 μm), a thick film through-hole conductor for electricconnection between the multi-layered wirings (Ag-1 wt % Pt, diameter 140μm) and a thermal via hole for heat dissipation (Ag-1 wt % Pt, diameter140 μm).

A thick film wiring pattern 104 (Ag-1 wt % Pt, thickness 15 μm) wasformed on one of the main faces of the multi-layered glass ceramicsubstrate 100. Chip components including the chip resistor 101 and chipcondenser 102 were coated with the paste used in example 2. The pastecomprises silver particles coated with hexylamine; the silver particleshaving the particle size of 100 nm or less have particle sizedistribution peaks at 7.6 nm and 15.2 nm and in a particle size of 100nm or more the silver particles have a peak of the particle sizedistribution at 2.75 μm. The silver particles having the above particledistribution peaks were dispersed in toluene at a concentration of 80%by weight. The paste was coated on the thick film pattern, followed bybonding at 300° C. for 5 minutes under a pressure of 0.5 MPa towards thechip components. As a result, the wiring pattern and the chip componentswere electrically connected by sintered silver layer 105.

MOSFET 1 (Si, temperature constant 3.5 ppm/° C.) was mounted In thecavity formed in one main face of the multi-layered glass ceramicsubstrate 100 by means of an intermediate member 103. Bonding wasconducted in a vacuum of 10⁻³. The size of the intermediate member 103was 2.8 mm×2.2 mm×0.2 mm. The sintered silver layer 105 for connectingMOSFET 1 and the intermediate metal member 103 and the bonding layer 106for connecting the intermediate metal member 103 and the multi-layeredglass ceramic substrate are formed by using the paste in example 2wherein the bonding materials are dispersed in toluene in theconcentration of 80% by weight.

The clip type connecting terminal 107 made of copper is bonded betweenMOSFET 1 and the thick film wiring pattern 104. The clip was pressed at0.1 MPa at 300° C. for 2 minutes.

A thick film exterior electrode 104′ (Ag-1 wt % Pt, thickness; 15 μm)was formed on the other main face of the multi-layered glass ceramicsubstrate 100. The thick film exterior electrode 104′ is electricallyconnected to the thick film through the inner wiring layer disposed inthe ceramic substrate 100 or through-hole wiring. The epoxy resin layer108 is formed on the other main face of the multi-layered glass ceramicsubstrate 100 to seal the mounted chip components.

Example 7

In this example non-insulated type semiconductor device to which leadframe for a mini-molded type transistor was used is explained.

FIG. 11 shows a cross sectional view of the mini-molded typenon-insulated semiconductor device according to this example.

Silicon transistor element 1 (size; 1 mm×1 mm×0.3 mm) as a semiconductorelement was bonded to the lead frame 600 (thickness 0.3 mm) made ofCu—Cu₂O composite material by a sintered silver layer 601 formed fromthe paste. The paste comprises silver particles coated with hexylamine;the silver particles having the particle size of 100 nm or less haveparticle size distribution peaks at 7.6 nm and 15.2 nm and in a particlesize of 100 nm or more the silver particles have a peak of the particlesize distribution at 2.75 μm. The silver particles having the aboveparticle distribution peaks were dispersed in toluene at a concentrationof 80% by weight.

A collector of the transistor element 1 was placed at the bonding side.The emitter and the base electrode were disposed at the opposite side ofthe bonding side. The paste was coated on the portion between the clipterminal 602 and lead frame 600, and the bonding was conducted at 250°C. for 2 minutes under a pressure of 1.0 MPa towards the clip terminal.The main portion of the semiconductor device including the transistorelement 1 and the clip terminal 602 was molded with epoxy resin 603 bytransfer molding. The tips of the lead frame 600 are separated from thelead terminals after the molding with epoxy resin is finished.

Example 8

LED was packaged on a substrate using the bonding material according tothe present invention. Better heat dissipation is expected than those ofthe conventional solder bonding or thermal conductive adhesives.

1. A bonding material comprising metal particles, which are coated withan organic substance having carbon atoms of 2 to 8, wherein the metalparticles comprise a first portion having a particle size of 100 nm orless, and a second portion having a particle size larger than 100 nm butnot larger than 100 μm, each of the portions having at least one peak ofa particle distribution, based on a volumetric base.
 2. The bondingmaterial according to claim 1, wherein the metal particles are at leastone member selected from the group consisting of gold, silver andcopper.
 3. The bonding material according to claim 1, wherein theorganic substance contains oxygen atoms, nitrogen atoms and/or sulfuratoms.
 4. The bonding material according to claim 1, wherein the organicsubstance is at least one organic compounds having a radical selectedfrom the group consisting of an alcohol group, amino group, carboxylgroup, carbonyl group, aldehyde group and sulfanyl group.
 5. The bondingmaterial according to claim 1, wherein a weight ratio of the firstportion in the total metal particles is larger than 0.001, but smallerthan
 100. 6. The bonding material according to claim 1, wherein themetal particles are dispersed in an organic solvent.
 7. The bondingmaterial according to claim 1, wherein the organic substance is a memberselected from the group consisting of alkyl amines, alkyl carboxylicacids, alkyl alcohols and suphanyl compounds.
 8. A bonding materialcomprising metal particles having an average particle size of 1 nm to100 nm as a first portion, and aggregated particles having a particlesize of 10 nm to 100 μm as a second portion, wherein the aggregatedparticles are an aggregate of the metal particles, and wherein each ofthe first portion and the second portion has at least one peak of aparticle distribution on a volumetric base.
 9. The bonding materialaccording to claim 8, wherein the metal particles and the aggregatedparticles are coated with an organic substance having carbon atoms of 2to
 8. 10. The bonding material according to claim 9, wherein the organicsubstance is at least one organic compounds having a radical selectedfrom the group consisting of an alcohol group, amino group, carboxylgroup, carbonyl group, aldehyde group and sulfanyl group.
 11. Thebonding material according to claim 8, wherein the metal particles andaggregated particles are at least one member selected from the groupconsisting of gold, silver and copper.
 12. The bonding materialaccording to claim 8, wherein a weight ratio of the metal particles inthe total amount of the metal particles and the aggregated particles islarger than 0.001, but smaller than
 100. 13. The bonding materialaccording to claim 8, wherein the metal particles and the aggregatedparticles are dispersed in an organic solvent.
 14. The bonding materialaccording to claim 8, wherein the organic substance is a member selectedfrom the group consisting of alkyl amines, alkyl carboxylic acids, alkylalcohols and sulphanyl compounds.
 15. A bonding material comprisingmetal particles, which are coated with an organic substance havingcarbon atoms of 2 to 8, wherein the metal particles comprise a firstportion having a mean particle size of 100 nm or less and a secondportion having a mean particle size of 10 nm to 100 μm, each of thefirst and second portions having at least one peak of particledistribution, based on a volumetric base, and wherein the second portionis composed of the metal particles aggregated from the metal particlesof the first portion, the metal particles in the second portion beingcovered with the organic substance.
 16. The bonding material accordingto claim 15, wherein the organic substance has a radical selected fromthe group consisting of amino group, alcohol group, carboxyl group,sulphanyl group, carbonyl group, aldehyde group and ester group.
 17. Thebonding material according to claim 15, wherein the metal particles aredispersed in an organic solvent.
 18. The bonding material according toclaim 17, wherein the organic substance is a member selected from thegroup consisting of alkyl amines, alkyl carboxylic acids, alkyl alcoholsand sulphanyl compounds.
 19. The bonding material according to claim 15,wherein the organic substance on the metal particles in the secondportion has been removed.
 20. The bonding material according to claim15, wherein the metal particles in the first portion have a meanparticle size of 1 nm to 100 nm, and the metal particles in the secondportion have a mean particle size of 100 nm to 100 μm.
 21. The bondingmaterial according to claim 15, wherein the metal particles coated withthe organic substance are suspending in an organic solvent.
 22. Thebonding material according to claim 15, wherein the organic substance isa member selected from the group consisting of alkyl amines, alkylcarboxylic acids, alkyl alcohols and sulphanyl compounds.